Deforsting controller for electric refrigerator

ABSTRACT

A defrosting controller for electric refrigerators which is operated under control of a first transistor adapted for triggering a silicon-controlled rectifier depending upon the result detected by a temperature detector in the freezer of the refrigerator and under control of a second transistor for keeping the first transistor in one state during the defrosting operation so that the defrosting operation is automatically stopped as soon as the temperature within the freezer reaches a predetermined temperature after starting the defrosting operation. Thus, frost accumulated within the freezing compartment can completely be removed and an unnecessary temperature rise within the freezing and provisions compartments can be prevented.

United States Patent Inventors Zenji Kusuda DEFORSTING CONTROLLER FOR ELECTRIC REFRIGERATOR 4 Claims, 2 Drawing Figs.

Int. Cl F2Sd 21/06 Field of Search 62/151,

[56] References Cited UNITED STATES PATENTS 3,222,882 12/1965 Suttom 62/156 3,248,892 5/1966 Sutton 62/156 3,363,429 l/ 1968 Wechsler 62/156 Primary Examiner-Meyer Perlin Attorney-Stevens, Davis, Miller & Mosher ABSTRACT: A defrosting controller for electric refrigerators which is operated under control of a first transistor adapted for triggering a silicon-controlled rectifier depending upon the result detected by a temperature detector in the freezer of the refrigerator and under control of a second transistor for keeping the first transistor in one state during the defrosting operation so that the defrosting operation is automatically stopped as soon as the temperature within the freezer reaches a predetermined temperature after starting the defrosting operation. Thus, frost accumulated within the freezing compartment can completely be removed and an unnecessary temperature rise within the freezing and provisions compartments can be prevented.

DEFORSTING CONTROLLER FOR ELECTRIC REFRIGERATOR This invention relates to a defrosting controller for electric refrigerators which controls electronically the defrosting operation of electric refrigerators and detects a variation in the temperature within the freezer during the defrosting operation, thereby automatically bringing the defrosting operation to an end.

It is commonly known that the cooling efficiency of an electric refrigerator is reduced when frost accumulates within the freezer, or more specifically, when frost deposits on the surface of the evaporator in the electric refrigerator. Various methods previously used for the removal of frost are such that a defrosting valve is opened for a predetermined period of time for circulating hot gas through the evaporator or a heater is placed in operation to generate heat for a predetermined period of time. However, the conventional defrosting methods in which the duration of the defrosting operation is thus predetermined and the defrosting operation is continued for a predetermined period of time independently of the amount of frost accumulated within the freezer have had certain inherent inconveniences. More precisely, even when only a small amount of frost is accumulated within the freezer, the defrosting operation is still continued after the frost has completely been removed resulting in a rise of the temperature in the provisions compartment to a point which is undesirably high, while when quite a large amount of frost is accumulated within the freezer, the defrosting operation is stopped before all the frost within the freezer can completely be removed.

It is therefore an object of the present invention to overcome the inconveniences encountered with these and other known defrosting systems and to provide a novel defrosting controller which brings the defrosting operation to an end by automatically stopping the heating operation of the defrosting heater or by automatically closing a hot gas circulating valve at the moment when frost accumulated within the freezer is completely removed.

The defrosting controller according to the present invention is adapted to perform the defrosting operation solely under a predetermined condition. More precisely, the defrosting operation is stopped at the moment when frost accumulated within the freezer is completely removed. Thus, the defrosting operation is always correctly performed irrespective of the relative amount of frost accumulated within the freezer. The above manner of defrosting operation completely eliminates the prior problem of an unnecessary and objectionable rise in temperature of the provisions compartment or imperfect removal of frost which has been inevitable with the conventional method of defrosting.

IN THE DRAWING:

FIG. 1 shows a first embodiment of the defrosting control circuit of the present invention;

FIG. 2 shows a second embodiment of the present invention.

Description of the defrosting controller according to the present invention will be made in conjunction with the accompanying circuit diagram of the defrosting controller employing a heater as heating means in one embodiment of this invention.

A thyristor, such as a silicon-controlled rectifier (called SCR hereinafter) is connected in series with a heating means disposed in a main circuit as shown in the drawings, and this SCR is urged to its conductive state or cutoff state'for closing or opening the main circuit thereby placing the heating means in operation when so required.

In FIG. 1, a heating means 3 such as a heater is connected with AC power source terminals 1 and 2. The means 3 may be a relay for driving a hot gas valve (FIG. 2). The defrosting controller comprises an SCR 4, a transistor 5 which is turned ON and OFF when the SCR 4 is ON and OFF, respectively, a DC bias supplying means 6 for the transistor 5, a thermistor 6 thermally coupled to the interior of the freezer for detecting a variation in the temperature within the freezer, a base bias dividing resistor 8, an emitter resistor 9 and a collector resistor 10 for the transistor 5, a rectifying diode 11, a smoothing capacitor 12, a voltage dividing resistor 13 for determining a base potential of the transistor 5 during the cooling operation, a switch 14 which is normally opened and is urged close momentarily in starting the defrosting operation, and a switch 15 which is normally opened and is urged close for bringing the defrosting operation to an end when required.

In the circuit described above, the SCR 4 is in its cutoff state and the switch 14 is in its open position in the normal state, that is, in the state in which no defrosting is required. Thus, since both the resistors 13 and 8 have relatively high resistances, little current flows in the circuit including the heater 3 therein and little heat is generated by the heater 3. In the above state, the AC power source voltage appears across the SCR 4, and the capacitor 12 is charged by the rectifying diode 11. The voltage appearing across the capacitor 12 is divided by the resistors 8 and 13 and applied to the base of the transistor 5. The emitter-base junction of the transistor 5 is reverse biased by the above voltage so that the transistor 5 is kept in its cutoff state. In order to keep the transistor 5 in its cutoff state, the voltage dividing ratio of the resistors 8 and 13 may be determined so that the voltage divided by the resistors 8 and 13, and applied to the base of the transistor 5 is higher than the output voltage of the DC power supply 6. Since the transistor 5 is kept in its cutoff state in such a manner as described above, no gate trigger current flows to the gate of the SCR 4 which is connected with the collector of the transistor 5, and the SCR 4 is still kept in its cutoff state.

The switch 14 may be closed to give the defrosting starting instruction to the defrosting control circuit which is kept in the state described above, thereby placing the defrosting control circuit in defrosting operation. The purpose can easily be accomplished by associating a means such as a timer withthe switch 14 so that the switch 14 can periodically be closed by the action of the timer.

Suppose now that the switch 14 is momentarily closed by the action of the timer. Then, a base current of the transistor 5 flows through an emitter resistor 9, the transistor 5 and the switch 14 to urge the transistor 5 into its conductive state. As a result, a gate trigger current flows to the gate of the SCR 4 to urge the same into its conductive state. This results in the closure of the main circuit comprising the AC power source terminal 1, heater 3, SCR 4, and AC power source terminal 2. The heater 3 is thus energized to start removal of frost accumulated within the freezer.

Since the SCR 4 is urged to its conductive state in a moment and the forward voltage drop across the conducting SCR 4 is quite small or in the order of a few volts, voltage of such a magnitude as will urge the transistor 5 to its cutoff state does not appear across the capacitor 12 when the switch 14 is forced open again. Thus, the transistor 5 is continuously kept in its conductive state and the defrosting control circuit is held in the operating state which is entirely the same as when the switch 14 is kept continuously closed. Therefore, the heater 3 continues to generate heat and the defrosting operation for the removal of frost within the freezer is continued.

As the frost accumulated within the freezer is removed, the temperature within the freezer rises gradually and the resistance of the thermistor 7 thermally coupled to the interior of the freezer decreases gradually. As a result, the emitterbase voltage of the transistor 5 obtained by dividing the voltage of the DC bias supplying means 6 by the thermistor 7 and the resistor 8 becomes low. At a point at which the temperature within the freezer reaches the defrosting ceasing temperature, the transistor 5 makes a transition from its conductive state to its cutoff state, resulting in a decrease of the gate trigger current supplied to the SCR 4.

Therefore, the conduction angle of the SCR 4 is now less than and there appears a phase in which no conduction takes place. 'The capacitor 12 is charged during the nonconduction phase of the SCR 4, and a voltage appears across the capacitor 12. This voltage is also applied to the base of the transistor so that the transistor 5 approaches its cutoff state more and more. In the meantime. so-called positive feedback occurs in the SCR 4, in which the gate trigger current is further reduced and the conduction angle of the SCR 4 becomes smaller. As a result, the transistor 5 is rapidly urged to its cutoff state and the SCR 4 is rapidly urged to the cutoff state to open the main circuit again and to stop the defrosting operation, that is, the heating operation by the heater 3.

After the transistor 5 is urged to the cutoff state and the SCR 4 is urged to the cutoff state, the temperature within the freezer is reduced. Since the base potential of the transistor 5 is the potential obtained by dividing the voltage charged across the capacitor 12 by the resistors 8 and 13, the transistor 5 does not conduit in spite of an increase in the resistance of the thermistor 7 and is kept in its cutoff state until the switch 14 is closed again. Thus, the circuit is kept in the state of cooling operation.

Suppose now that the switch 15, which is added in order to urge the controller under defrosting operation into cooling operation, is closed during the defrosting operation, then thermistor 7 is short-circuited. This is equivalently the same state as in the case where the resistance of the thermistor decreases. As a result, the defrosting operation is stopped.

The above description has been directed to the case of employing the heater 3 as a defrosting means. However, the heater 3 may be replaced by a relay 16 connected in series with the SCR 4, as shown in H6. 2, which relay serves to open the hot gas circulating valve. In this case, the conduction of SCR 4 causes a current to flow through a winding of the relay 16, thereby actuating the relay 16. As a result, the hot gas circulating valve (not shown) is opened to thereby remove the frost produced within a refrigerator in the same manner as mentioned above.

We claim:

1. A defrosting controller for an electric refrigerator having a defrosting heater means, a silicon-controlled rectifier for controlling the operation of said defrosting heater, and control means for triggering said silicon-controlled rectifier, said control means being urged to its conductive state and to its cutoff state when said silicon-controlled rectifier is in its conductive state and cutoff state, respectively, said control means com prising a transistor the collector of which is connected with the gate of said siliconcontrolled rectifier, a charging means composed of a diode and a capacitor which is connected in parallel with said silicon-controlled rectifier, a voltage dividing means which divides the voltage obtained by said charging means sand applies the divided voltage to the base of said transistor and DC bias supplying means for supplying a DC bias voltage to said transistor, wherein a temperature detector thermally coupled to the freezer is connected with the base of said transistor as a base bias dividing resistor and a switch adapted to be closed to start the defrosting operation is connected between the base of said transistor and an AC power line.

2. A defrosting controller according to claim 1, in which said temperature detector is a thermistor.

3. A defrosting controller according to claim 1, in which said voltage dividing means comprises resistors connected in series.

4. A defrosting controller for an electric refrigerator having a defrosting relay means for controlling a hot gas flow, a silicon-controlled rectifier for controlling the operation of said defrosting relay means, and control means for triggering said silicon-controlled rectifier, said control means being urged to its conductive state and to its cutoff state when said siliconcontrolled rectifier is in its conductive state and cutoff state, respectively, said control means comprising a transistor the collector of which is connected with the gate of said siliconcontrolled rectifier, a charging means composed of a diode and a capacitor which is connected in parallel with said silicon-controlled rectifier, a volta e dividing means which divides the voltage obtained by sar charg ng means and applies the divided voltage to the base of said transistor, and DC bias supplying means for supplying a DC bias voltage to said transistor, wherein a temperature detector thermally coupled to the freezer is connected with the base of said transistor as a base bias dividing resistor and a switch adapted to be closed to start the defrosting operation is connected between the base of said transistor and an AC power line. 

1. A defrosting controller for an electric refrigerator having a defrosting heater means, a silicon-controlled rectifier for controlling the operation of said defrosting heater, and control means for triggering said silicon-controlled rectifier, said control means being urged to its conducTive state and to its cutoff state when said silicon-controlled rectifier is in its conductive state and cutoff state, respectively, said control means comprising a transistor the collector of which is connected with the gate of said silicon-controlled rectifier, a charging means composed of a diode and a capacitor which is connected in parallel with said silicon-controlled rectifier, a voltage dividing means which divides the voltage obtained by said charging means sand applies the divided voltage to the base of said transistor and DC bias supplying means for supplying a DC bias voltage to said transistor, wherein a temperature detector thermally coupled to the freezer is connected with the base of said transistor as a base bias dividing resistor and a switch adapted to be closed to start the defrosting operation is connected between the base of said transistor and an AC power line.
 2. A defrosting controller according to claim 1, in which said temperature detector is a thermistor.
 3. A defrosting controller according to claim 1, in which said voltage dividing means comprises resistors connected in series.
 4. A defrosting controller for an electric refrigerator having a defrosting relay means for controlling a hot gas flow, a silicon-controlled rectifier for controlling the operation of said defrosting relay means, and control means for triggering said silicon-controlled rectifier, said control means being urged to its conductive state and to its cutoff state when said silicon-controlled rectifier is in its conductive state and cutoff state, respectively, said control means comprising a transistor the collector of which is connected with the gate of said silicon-controlled rectifier, a charging means composed of a diode and a capacitor which is connected in parallel with said silicon-controlled rectifier, a voltage dividing means which divides the voltage obtained by said charging means and applies the divided voltage to the base of said transistor, and DC bias supplying means for supplying a DC bias voltage to said transistor, wherein a temperature detector thermally coupled to the freezer is connected with the base of said transistor as a base bias dividing resistor and a switch adapted to be closed to start the defrosting operation is connected between the base of said transistor and an AC power line. 